In 1965 neurophysiologists Ronald Melzack and Patrick Wall described what became known as the ‘Gate Theory’ of sensation, principally painful sensation. (Melzack R, Wall P D: Pain mechanisms: A new theory. Science 150:971,1965.) Basically they showed that input signals from painful stimuli, on reaching the spinal nerves, via normal connecting nerve fibers, were subjected to an anatomical ‘gate’ or switch in a specific part of the spinal cord. This gate, by incoming signal type and intensity, determined if the signals would be passed up the spinal cord to the sensory areas of the brain or locally blocked. Painful stimuli of sufficient intensity and arising from specific areas from peripheral injuries are passed by this ‘gate’ if unopposed by other sensory input; this mechanism alerts the patient to potential or actual tissue injury. These investigators proved that non-painful stimuli of sufficient amplitude and from similar locations as the pain source could ‘close’ the ‘gate’ to the painful signals, blocking their transmission upward to conscious experience. It was shown in experiments and later in very large clinical application that electrical ‘tingling’ stimuli could inhibit the experience of pain. On this concept a substantial industry was built using electrical stimulation for pain control. Further, the gate theory showed that other non-painful stimulus, such as vibration or distraction through massage or the application of liniment, heat or cold to the overlying skin in many parts of the body including the face and head, could likewise inhibit the sensation of pain in the same areas. Distant distraction of pain is also well known. For example, the ancient practice of ‘biting on a bullet’ or clenching objects during childbirth is related to such inhibition by a conflicting sensory input although at a different location in the central nervous system. Additionally, acupuncture may provide the distracting sensation that can reduce pain perception. These phenomena had long been known but the scientific proof and understanding had been lacking until the work by Melzack and Wall and many subsequent investigators.
For dental pain suppression, pulsatile electrical stimulation of gums, tongue or roof of the mouth is potentially useful but not practical due to the easy dislodgment of the electrodes which might otherwise unfortunately need to be firmly attached, perhaps by sewing to the tissues or cyanoacrylate gluing to the surfaces of these structures. Further should the location of stimulation might need changing during the procedure, it would be difficult if using tissue-attached electrical stimulator electrodes. Teeth are supplied with pain fibers that also weakly detect temperature and pressure changes; however, gums and adjacent soft tissues are sensitive to electrical stimulation, touch and vibration.
One known approach to inhibit periodontal pain is practiced in a simple but limited form by dentists when they rapidly and intermittently tug gently on teeth or lips near the site of a needle puncture during, for example, infiltration of local anesthesia into and through the gums. This tugging distracts the sensation of immediate pain of the needle stick and passing of the needle through the gum, aiming at the dental nerve at its entrance to the root of the tooth or teeth. Other methods of distraction are also employed such as music or white noise provided through patient earphones or even electrical stimulation of the face. A local surface anesthetic material may be applied to the gum before the needle enters but this does not help for deeper passage of the needle or during the surgical procedure.
With the above Background in mind, improvements to, and advancement of, pain suppression during dental surgery will be welcomed by both dental caregivers and by patients.